Python converting from c# Calculating CRC8 from 4/5 bytes frame

Question

I've got a frame build like this : {0x00, 0x00, 0x00, 0x00, 0x00}.

C# script to calculate crc8

   u8 Crc(u8 *buffer, u8 length) 
   {
        u8 crc = 0, idx;
        while ( length-- != 0 ) 
        {
            crc = crc ^ *buffer++;
            for ( idx = 0; idx < 8; ++idx ) 
            {
                if ( crc & 0x01 ) crc = (crc >> 1) ^ 0x8C;
                else crc >>= 1;
            }
       }
       return crc;
    }

can someone show me how to write it correctly in Python?

Where did you get this crc8 algorithm? The bitshift directions and polynomial seem odd. — jedwards
– jedwards, Commented Jun 15, 2018 at 11:16

PM 2Ring · Accepted Answer · 2018-06-15 11:26:12Z

2

The site you linked appears to use the same algorithm as what you've posted. It's easy enough to translate to Python, all of the bit twiddling code remains the same, all you need to change is the code that loops over the input buffer.

def crc8(buff):
    crc = 0
    for b in buff:
        crc ^= b
        for i in range(8):
            if crc & 1:
                crc = (crc >> 1) ^ 0x8C
            else:
                crc >>= 1
    return crc

buff = [0x12, 0xAB, 0x34]
crc = crc8(buff)
print(hex(crc))

output

0x17

This code also works correctly if buff is a bytes or bytearray object.

edited Jun 15, 2018 at 11:26

answered Jun 15, 2018 at 11:20

PM 2Ring

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